The set up and calibration of thermal transfer printers can be both cumbersome and expensive. In most thermal transfer printers, full calibration requires feeding several feet of label stock and ribbon material. This calibration process must be performed each time a different type of media is loaded into the printer. The set up and calibration process can be avoided if the printer can discern what type of media is loaded.
To simplify printer set-up, various methods have been used to identify the media loaded into a thermal transfer printer, including touch cell memory components and barcodes. In these applications, a code or memory component including media identification data is coupled to the media provided in the printer. The data is read when the media is positioned in the printer, and the printer is configured for the appropriate media.
One method that is particularly well-suited for identifying media in a thermal transfer printer is radiofrequency identification or RFID technology. Unlike barcode or touch cell memory applications, RFID does not require either a line of sight or a direct connection to the identifying code or memory component to acquire data about the media loaded into the printer.
Antenna systems used in these types of printers for reading the data from the RFID tags, however, typically comprise a single horizontal coil or loop antenna housed in the media spindle of the printer. When the RFID transponder travels around the circumference of such an antenna, there are null areas at which the RFID reader cannot download information from the RFID transponder associated with the tag. These null areas occur when the RFID tags are perpendicular to the plane of the antenna, and, although the width of the null areas can be varied, they can never be eliminated. These nulls create problems if the printer attempts to gather information from the RFID transponder while the transponder is located in a null. This problem is particularly troublesome when the media is initially loaded into the printer, and when it is important to verify the type of media inserted into the printer.
The present invention addresses these problems.